Timber and concrete upper floors

6.4

6.4.14Timber joist and restraint strap

Upper floors shall provide adequate lateral restraint.

Restraint straps and joist hangers suitable for taking tensile forces may be required to tie walls and upper floors together or when the external wall is stabilised by a connection to the floor. Straps should:

be detailed in the design, including the size, position and fixings

be galvanised steel with a 30mm x 5mm cross-section or be in accordance with Technical Requirement R3

have adequate packing between the wall and the first joist

bear on the centre of bricks or blocks and not on mortar joints

be fixed on the side, top or bottom, as appropriate to the joist type.

Restraint straps should be provided along the direction of the joists and spaced at a maximum of 2m centres. They are not generally required at the ends of joists in buildings up to, and including, two storeys where:

restraint type joist hangers in accordance with Technical Requirement R3 are used, or

joists are built into a wall and bear at least 90mm on the wall.

Where joists run parallel to the wall, straps should be fitted along the joists with a maximum spacing of 2m, and:

be supported on noggings and extend over at least three joists

be fixed with two screws or nails into each joist

have noggings provided to receive two additional nails (for solid joists, two 4.76mm diameter x 50mm long wood screws (No.10) or 4mm diameter x 75mm round nails (8 SWG) can be used in each joist).

Solid timber joists

Solid timber joists should, have noggings provided at:

a minimum of 0.5 x the depth of the member when straps are located on top of the joist, or

the full depth of the member where straps are located beneath the joist.

I-joists

I-joists should not be notched and have:

solid timber noggings no less than 0.5 x the depth of the member and a maximum of 150mm fixed between the webs and located beneath the top flange, when 30mm x 5mm galvanised straps are used, or

noggings made from short lengths of I-joist, or solid timber the full depth of the I-joists, when proprietary straps are used.

When nailing into laminated veneer lumber flanges:

care should be taken to prevent splitting

nails should be driven in at an angle (not horizontally) and should not protrude from the flanges.

Metal web joists

Metal web joists should not be notched and should have:

35mm x 97mm solid timber noggings beneath the top flange of the metal web joists, and

noggings nailed twice to each joist.